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Objective:
Since antibiotics are neither recommended nor used for STEC treatment in humans or carrier-animals, strategies as described in the National Strategy for Combating Antibiotic Resistant Bacteria (CARB; 1) are needed and will be investigated for STEC control in cattle as exemplified in the following objectives:
Objective 1: Understand the impact of the bovine intestinal environment, especially at the rectoanal junction, and the molecular mechanisms that promote or inhibit colonization, adherence, and persistence of STEC in cattle and develop intervention strategies to control STEC colonization.
Subobjective 1A: Identify bacteria in the rectoanal junction (RAJ) microbiome that could effectively interfere with STEC colonization for possible use in probiotic applications.
Subobjective 1B: Identify bacterial ligands and tissue receptors involved in STEC adherence to the RAJ.
Objective 2: Formulate and assess the efficacy of vaccines for controlling STEC colonization of cattle based on whole-cell and subunit vaccines and identify proteins and epitopes conserved in STEC.
Objective 3: Define potential biomarkers using systems-based approaches that will allow the development of rapid diagnostic tests to identify STEC-colonized cattle.

Approach:
Experimental animal and animal organ/tissue culture models will be used for determining qualitative and quantitative changes in bacterial communities constituting the rectoanal junction (RAJ) and fecal microbiomes, in response to colonization of cattle intestines by STEC serotype O157:H7 (O157). These microbiome changes will be correlated with the duration and magnitude of fecal O157 shedding by colonized cattle and compared to fecal/RAJ microbiome of non-colonized cattle. The results from these comparative studies will be used for identifying bacterial species that are part of the cattle intestinal microbiome and can compete effectively with O157 for bovine intestinal colonization. In vitro organ and tissue culture systems will be used for evaluating effects of these bacteria on O157 colonization at the RAJ. Proteomics-based techniques will be used for identifying proteins that are used by O157 to adhere to RAJ epithelial cells. Analogs mimicking these proteins will be designed and evaluated for their ability to interfere with O157 adherence to the RAJ epithelial cells. The existing O157 mutant vaccine strain will be modified and will be used as a whole-cell killed vaccine for determining if vaccination of cattle with the modified vaccine would show increased efficacy in controlling O157 colonization of cattle compared to the unmodified mutant strain-based vaccine. Metabolomics-based techniques will be used to identify metabolites present in blood samples of O157-colonized and non-colonized cattle. Few metabolites that are uniquely present in O157-colonized cattle will be evaluated for use as biomarkers to differentiate such cattle from the non-colonized animals.